<!DOCTYPE html>
<html>
<head>
  <title></title>
  <script src="https://cdn.bootcss.com/rxjs/6.3.3/rxjs.umd.min.js"></script>
</head>
<body>
<script type="text/javascript">
  // const source$ = rxjs.of(1,2,3);
  // source$.subscribe(console.log);
  const onSubscribe = observer => {
    observer.next(1);
    observer.next(2);
    observer.next(3);
  }
  const source$ = new rxjs.Observable(onSubscribe);
  const theObserver = {
    next: item => console.log(item)
  }
  source$.subscribe(theObserver);
</script>
</body>
</html>